Neat topology from messy model
If the purpose of doing a model is learning, start from scratch. Plan your topology carefully. Add detail where is needed and keep it simple where is supposed to be simple. Try as much as possible to keep your topology as
 quads. You will spend less time in a carefully planned model than trying to fix something that is poorly put together.

Adding to what @DuarteFarrajotaRamos said, topology should not be an afterthought or some form of wrapper, but the model itself.